Microsoft word - van rossum & prentice

Morphological and allozyme variation of Silene nutans
(Caryophyllaceae) at the northwestern margin of its distribution

Fabienne Van Rossum1, Honor Prentice2
1National Botanic Garden of Belgium, Department of Vascular Plants, Domein van Bouchout, B-1860
Meise, Belgium
2Lund University Plant Ecology and Systematics, Department of Ecology, Sölvegatan 37, S-22362 Lund, Sweden With the collaboration of the Université Libre de Bruxelles, Laboratoire de Génétique et Ecologie Végétale, Belgium Silene nutans L. (Caryophyllaceae) is an insect-pollinated, long-lived perennial herb occurring on rock outcrops in dry, thermophilous grasslands, open forests and forest edges. It shows a continental distribution range extending from northwestern Europe to central Siberia and the South-Caucasus. At the western and northern margins of its European range, it shows a disjunct and scattered distribution. The study of allozyme and morphological (leaf shape, fruit size) variation of range-margin populations, from Belgium, France, Sweden and NFinland reveals divergence among populations. On the one hand, the populations in Belgium are differentiated into two parapatric edaphic ecotypes, calcicolous and silicicolous. These ecotypes, which occur in different, contiguous but not overlapping ecological niches, show contrasted leaf shape and fruit size, and can be distinguished into two different gene pools based on allozymes. In France, there is no indication of ecotypic differentiation but two geographical groups, peripheral and central, could be distinguished based on allozymes and fruit size. The peripheral populations were genetically closely related to the Belgian silicicolous ecotype. The central populations were closer to the Belgian calcicolous ecotype, but yet significantly differentiated for allozyme and morphological traits. This suggests an ancient differentiation and different migration histories for the Belgian ecotypes. Belgium may constitute a contact zone between the two groups, and adaptive radiation may have occurred owing to geological heterogeneity (presence of calcareous and siliceous bedrocks). They may also represent unique genetic patterns for the species and may be of great value from a conservation point of view. In Sweden and NFinland, two groups can be identified based on allozyme and leaf shape patterns, suggesting two major postglacial immigration routes, from south and east, and a contact zone with admixed populations in central Sweden. Moreover, these populations differ in morphological traits (leaf shape, fruit size) from the western populations. In conclusion, the results on allozyme and morphological variation at the northwestern margin of its distribution range suggest a quite complex pattern of the geographic structuring of genetic variation of S. nutans, likely shaped by past migration history but also by ecological specialization and recent processes. The phylogeographical study of the European populations of S. nutans using cytoplasmic DNA markers (mtDNA and cpDNA) currently in progress (see the poster of S. Le Cadre et al.) will certainly contribute to elucidate the relative contributions of historical and recent processes (e.g. selection) to present-day genetic structure and to define potential Evolutionarily Significant Units (ESU). Correspondence:



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